Shirley tries to convince herself that she's not missing out by not having friends, but she knows she's wrong.
One day, when she leaves school, she bumps into the scariest girl in the entire grade: Mabel. Mabel insults her, but Shirley doesn't back down, so the bully punches her and Shirley gets two black eyes. When she gets home, though, Shirley refuses to spill the beans. Honor code, right?
Her parents want to go to the police, but Shirley sees Mabel, who's hinting at her not to confess.
Shirley stays home from school for a few days, but when she returns, she comes across Mabel again. But guess what? Instead of throwing punches, Mabel's actually being nice now, perhaps because Shirley didn't rat her out, and later even invites our main girl to play stickball.
Mabel's friends insult Shirley, but Mabel insists that Shirley be on her team, bullying the others into it. She tries to teach Shirley the rules of stickball, and Shirley slowly catches on, bit by bit.
Inadvertently, she scores a run, and her teammates are stoked, even cheering for her. She's so happy about this that stickball is now her favorite game.
And she gets better, thanks to Mabel's teaching (she also teaches Shirley to skate).
Needless to say, Shirley's pretty happy she didn't rat out Mabel, because now she's got the friendship and protection of the biggest girl in the grade.